ltfrankcastle:

What strikes me the most about Frank knowing that Karen had a gun in her bag, is the fact that it isn’t even her gun. Billy took her gun as a preventive security measure for the senator, which she would get back upon leaving the building. The gun in her bag was picked up from the floor, probably one of the dead Anvil men’s, and shoved into her bag on the way out. Frank knew without a shadow of a doubt that Karen had a gun, maybe not hers but a gun, in her bag and was willing to use it.

Frank knows Karen.